Methods of producing large steel ingots

ABSTRACT

A method of producing large steel ingots is provided combining the steps of pouring an ingot in the conventional manner, solidifying the same, removing an axial core lengthwise of said ingot to form a central cavity and filling the cavity with metal from an electrode by electroslag remelting.

United States Patent l 72] Inventor Lloyd R. Cooper Pittsburgh, Pa. 1 21Appl. No. 797,944 [22] Filed Feb. 10,1969 [45] Patented Sept. 7, 1971[73 Assignee Heppenstall Company [54] METHODS OF PRODUCING LARGE STEELINGOTS 3 Claims, 1 Drawing Fig.

[52] US. Cl 164/52, 29/5265 [51 Int. Cl 822d 27/02 [50] Field ofSearch164/52, 50, 252, 53; 29/5264, 5265 [56] References Cited UNITED STATESPATENTS 1,207,572 12/1916 Law et a1. 164/252 2,230,296 2/1941 Hopkins164/52 2,240,405 4/ l 941 Kinzel 164/52 2,248,628 7/1941 Hopkins 164/523,482,259 12/1969 Schwarz 164/52 X FOREIGN PATENTS 833,122 7/1938 France164/52 107,798 6/1939 Australia 164/50 107,405 5/1939 Australia 164/52503,716 4/1939 Great Britain 164/50 Primary Examiner-J. SpencerOverholser Assistant ExaminerV. Rising Att0rneyBuell, Blenko &Ziesenheim ABSTRACT: A method of producing large steel ingots isprovided combining the steps of pouring; an ingot in the conventionalmanner, solidifying the same, removing an axial core lengthwise of saidingot to form a central cavity and filling the cavity with metal from anelectrode by electroslag remelting.

PATENTEDSEP Han. 3503374 INVIEN'I Lloyd R. oper METHODS OF PRODUCINGLARGE STEEL IllGOTS This invention relates to methods of producing largesteel ingots and particularly to a method for producing ingots toprovide a solid large ingot free of the central cavity or pipe which isa common problem in the casting of large ingots. This problem of pipingin ingots is one which is well known to the steel industry but is ofparticularly great importance in casting large cross section ingots.

In the production of steel ingots for subsequent forging or rollingoperations, the conventional method consists of teeming the liquid steelinto chilled iron molds of the desired cross sectional area and heightto contain the liquid steel, and to produce a solid steel ingot whichcan be heated and handled for the forging or rolling operation.

It is well established that steel which has been fully deoxidized (bysuch metal deoxidizers as silicon or aluminum or by carbon underconditions of low pressure) will occupy less volume after solidificationthan it did in the liquid form. Since the metal next to the sidewallsand bottom of the molds solidifies first, the liquid metal in thecentral portion of the ingot, which solidifies last, will shrink andoccupy less final space with unacceptable shrinkage voids unless asatisfactory means is employed of providing additional liquid steel toovercome this final shrinkage mechanism. The use of refractory lined orexothermic sinkheads or hot tops is a well established practice in theart in the effort to assure sound ingot centers.

This method of producing sound ingots of killed steel is generallyconsidered to be satisfactory for smaller ingot cross sections andweights, i.e. up to 20 inches to 30 inches diameter or thickness ofingot, weighing up to or tons total weight. On larger ingots, however,the time required for complete solidification of the ingot becomesincreasingly longer as the ingot cross section increases, so that manyhours elapse between the teeming of the liquid steel and the final totalsolidification of the steel at the ingot axis. As this elapsed time mayexceed 10 hours or 20 hours or even hours, the reservoir of liquid steelin the sinkhead or hot top becomes ineffective to feed into theshrinkage cavities in the ingot body, and a central cavity or piperesults. It thus becomes increasingly difficult and impractical toguarantee sound ingot bodies when the ingot diameter or cross-sectionaldimension exceeds 50 inches, and the total ingot weight exceeds 50 tonsor more.

In recent years, the process of Electroslag Remelting" of steel ingotsor electrodes has been developed for many chemical compositions ofsteel, high temperature alloys and other metals. In this remeltingprocess, a solid steel electrode is melted progressively with the heatgenerated by the electrical resistance of a liquid slag to electriccurrent passing through the steel electrode to the liquid slag, andthence to another electrode or to the resolidifying ingot and crucibleor mold which contains the resolidifying ingot. The steel, which isprogressively melted from the electrode, passes in liquid form throughthe liquid slag and collects in a pool of liquid steel below the liquidslag layer. The pool of liquid steel solidifies progressively so that atany one time of the remelting operation, it is a pool of liquid steelwhiehrepresents only a small portion of the total weight of electrode(s)or steel ingot that is resolidified. In this process it has been wellestablished that the large axial shrinkage voids of conventionallyteemed ingots are avoided by the Electroslag Remelting andresolidification process.

The Electroslag Remelting process has been used for alloy steel ingotsas large as 46 inches in diameter, and designs are being engineered forElectroslag Remelting of ingots larger than 100 inches in diameter ofproportionate heavy weights. However, these extra large remeltingfacilities require power supplies and electrical systems for control ofmelting rate, which present an economic block to the practicality of theremelting system.

The invention described here makes use of a combination of conventionalingot teeming with the Electroslag Remelting system for assuring theproduction of the largest forging ingots with the center soundnesscharacteristics of Electroslag Re melted ingots at a much lower cost forcapital equipment and operating expense.

In this invention, a conventional large forging ingot is teemed into amold with refractory lined or exothermic sinkhead, according to presentpractices. After this steel solidifies, an axial cavity is formedthroughout the full length of the solidified ingot. The diameter of thiscavity will be in order of 20 percent to 35 percent of the outsidediameter of the ingot, and may be formed by trepan boring cold, trepanpunching under a press, or drift punching under a press.

In the case of trepan boring or trepan punching, it is intended that thecore, thus removed, would be forged to a smaller diameter to furnishelectrodes for Electroslag Remelt' ing within the cavity formed byremoval of the core.

In the case of the drift punching operation, it is realized that themajority of the center material of the ingot will be dis placedlaterally to the location adjacent to the inside surface of the punchedhole. In this case, the metal for the electrode to be used inElectroslag Rcmelting will be furnished from another ingot from the samemelt or from another melt of the same nominal composition as the largeingot.

The inside surface of the cavity in the bored or punched ingot will beprepared by shot blasting or machining to assure freedom from excessiveoxide. The electrode will be similarly prepared by casting, forgingand/or sh-ot blasting, or machining. The electrodes may be in severallengths of sufficient weight to completely fill the axial ingot cavityas well as starting pool and hot topping volume.

The ingot is set up in the remelting station. as shown in theaccompanying Figure, showing a vertical section of an ingot according tothe invention with the remelting operation partially completed. Theoriginal ingot 10 is prepared by coring or punching an axial hole 11through the full length. In the illustration, the original ingotsinkhead is shown as being integrally cored or punched with the ingotbody. In practice this sinkhead may also be removed, and another moresymmetrical block be used for the electroslag hot topping. The hollowingot l0, preheated to the proper temperature range, is positioned onthe preheated starting block 12, and the prepared electroslag 13 isadded (powdered or liquid condition). The electrode 14 is lowered intoposition, and the power turned on. The electrically heated liquid slagmelts the end of the electrode as well as an adjacent zone of the ingotmetal, as indicated by the depth of penetration" 17. In the partiallycompleted cycle shown in the Figure, the liquid slag 13 has melted steelfrom the end of the electrode (at 15), forming the shallow pool ofliquid steel 16 containing steel from the electrode and from theadjacent portion of the ingot. The depth of penetration 17 of the liquid(and resolidified) steel, is controlled by the power input and thepreheat temperature range of the ingot body. The diameter of totalremelted metal normally represents one-third to one-half of the diameterof the original ingot cross section, although greater or smaller ratiosmay be obtained by controlling the power input, and preheatingparameters.

The economics of this invention become readily apparent when it isrealized that the power requirement for melting the inner core equal toone-third of the total ingot diameter is only slightly more than 10percent of that required for electroslag remelting the entire ingot atthe large overall diameter.

This application of the combination of conventional teeming andElectroslag Remelting produces large cross section ingots completelyfree from the central porosities or cavities, as well as the excessivechemical segregation found in conventionally teemed ingots. It bringsthe practice of Electroslag Remelting within ready economicconsideration, as compared with the complete remelting of exceptionallylarge and heavy forging ingots.

This invention is also readily applied to the production of largecomposite ingots of different chemical compositions between the innercore" and the outer shell" of the composite ingot. In this application,the penetration or mixing. of the steel from the electrode compositioninto the steel of the initial ingot composition, is kept to a minimum bya lesser preheating temperature range for the starting block and ingot,and a corresponding control of the power input and melting rate of theelectrode material.

While I have illustrated and described a presently preferred practice ofmy invention in the foregoing specification, it will be understood thatthis invention may be otherwise embodied within the scope of thefollowing claims.

I claim:

I. The method of producing large steel ingots comprising the steps of:

a. casting a steel ingot to the final desired size,

b. removing an axial core lengthwise of said cast ingot to form acentral cavity,

c. melting a steel electrode formed from the core removed from the ingotwithin said central cavity under a fused slag by passing an electricalcurrent through said electrode within the cavity to the ingot, and

d. solidifying the melted electrode metal within the cavity to form asolid ingot mass.

2. The method of claim I wherein the axial core is removed by punchingsaid core from said ingot.

3. The method of claim 1 wherein the axial core is removed by trepanningsaid core from the ingot.

1. The method of producing large steel ingots comprising the steps of:a. casting a steel ingot to the final desired size, b. removing an axialcore lengthwise of said cast ingot to form a central cavity, c. meltinga steel electrode formed from the core removed from the ingot withinsaid central cavity under a fused slag by passing an electrical currentthrough said electrode within the cavity to the ingot, and d.solidifying the melted electrode metal within the cavity to form a solidingot mass.
 2. The method of claim 1 wherein the axial core is removedby punching said core from said ingot.
 3. The method of claim 1 whereinthe axial core is removed by trepanning said core from the ingot.